1. Field of the Invention
The invention relates to field emission lamps and, particularly, to a carbon nanotube-based field emission lamp.
2. Description of Related Art
A display device, such as a LCD, often requires a backlight device installed at a rear side thereof to provide illumination. Typically, a cold cathode fluorescent lamp (CCFL) has been commonly used as a light source of the backlight device. The CCFL includes a sealed tube and a pair of electrodes respectively disposed at two ends of the sealed tube. A fluorescent layer is coated on an inner surface of the sealed tube. The sealed tube is filled with a mixture including an inert gas and a mercury-based substance. When electric voltage is applied to the electrodes, electrons are emitted and cause the mercury-based substance to discharge, thereby ultraviolet radiation is generated. The ultraviolet, in turn, strikes the fluorescent layer to result in visible radiation. However, the mercury-based substance, a prominent component of CCFL, is harmful to people and is a potentially dangerous pollutant.
Therefore, a field emission lamp, without using the mercury-based substance to achieve illumination, has been explored as an alternative light source for the backlight device. The field emission lamp includes a cathode electrode and an anode electrode disposed opposite to each other. An electron emitting layer is disposed on the cathode electrode. A fluorescent layer is disposed on the anode electrode and corresponding to the electron emitting layer. When a predetermined voltage is applied to the cathode electrode and the anode electrode, electrons emitted from the electron emitting layer collide against the fluorescent layer, and thereby visible light is generated.
As mentioned above, in such a backlight device using the field emission lamp, visible light is emitted in all directions from the fluorescent layer. That is, emitted light is not controlled to illuminate toward a particular direction.
What is needed, therefore, is a field emission lamp having high luminous efficiency to provide high luminance and in which light is emitted in a controlled, predetermined direction.